The embodiments described herein relate generally to modular processing assemblies, and more particularly, to methods and systems for selectively processing a flow back composition that is discharged from a well head.
As global demand for petroleum and natural gas production grows, the industry will continue to exploit more challenging oil and gas reservoirs, and in particular, reservoirs that may be considered uneconomical due to low formation permeability. Currently, hydraulic stimulation, known as hydro-fracturing, is accomplished using water-based fracturing fluids, wherein a pressurized liquid fractures a geological formation. Typically, water is mixed with proppants, which are solid materials, such as sand and aluminum oxide, and the mixture is injected at high pressure into a wellbore to create small fractures within the geological formation along which fluids such as gas, petroleum, and brine water may migrate to the wellbore. Hydraulic pressure is removed from the wellbore, and then small grains of proppant hold the fractures open once the geological formation achieves equilibrium. As the fracturing fluid flows back through the wellbore, the fluid may consist of spent fluids, natural gas, natural gas liquids, and petroleum and brine waters. In addition, natural formation waters may flow to the wellbore and may require treatment or disposal. These fluids, commonly known as a flowback composition stream, can be managed by surface wastewater treatment.
Hydro-fracturing may include potential environmental considerations, including treatment of large volumes of contaminated water produced during the flowback stage and an increased demand on local freshwater supplies, particularly in arid or otherwise water-stressed areas. Therefore, a need for large volumes of clean water for hydro-fracturing may preclude implementation in some locales. Hydro-fracturing may also pose technical risks relating to water-sensitive reservoirs.
At least some known conventional fracturing procedures have replaced water as the pressurized fluid with other fluids such as carbon dioxide, nitrogen, foams, and/or liquid propane. While these fluids, in comparison to water, provide a means for higher initial production rates and ultimate recovery of the reservoir hydrocarbons, some process challenges may exist associated with handling the post-stimulation flowback stream when using these fluids which can be volatile under ambient temperature and pressure conditions. These challenges include high variability in flow rates as well as gas compositions. The post-stimulation flowback rate is typically very high initially and may decrease by a few orders of magnitude over a period of a few days. Additionally, the gas composition may vary significantly. For example, for a well stimulated with carbon dioxide, the concentration of carbon dioxide in the flowback gas can be high initially such as, for example, over 90% volume, and decrease by an order of magnitude over a period of a few days. A conventional method to accommodate the high flow rates and variability when using these normally volatile fluids is to vent the flowback gas to the atmosphere with no recovery procedure, at least for the first few days of flowback operation. Such venting of these gaseous forms may result in inefficient use of the fluids and/or negative environmental impacts.